Noise caused by another car-mounted appliance is apt to be mixed into a signal input/output to/from an AM or FM receiver mounted in a car. Accordingly, various types of noise removing circuits are conventionally adopted. As one of examples, there is a method removing noise by extracting a noise component from a signal, by masking part of the signal, which corresponds to the noise component, and by holding the voltage of the immediately preceding input signal. With this method, a pulse signal is generated to mask the noise. However, if attempts are made to mask the noise, timing when the noise occurs and timing when the pulse signal generated based on this noise occurs must be made to match. Since a predetermined amount of time is naturally required to generate the pulse signal, an analog delaying circuit delaying the signal from which the noise is to be removed by the predetermined amount of time becomes necessary. Conventionally, a plurality of stages (such as 4 stages) of Bessel type filters are used as this analog delaying circuit.
In the meantime, since the above described Bessel type filters are configured by combining a resistor, a capacitor, and an operational amplifier, the whole of the analog delaying circuit, namely, the whole of the noise removing circuit cannot be formed on a semiconductor substrate if the device constants of the resistor and the capacitor are considered. Especially, even if a resistor and a capacitor, which have a large device constant, are formed on a semiconductor substrate, variations in the device constants of the resistor, etc. formed on the semiconductor substrate are large. Therefore, the delay time of the analog delaying circuit significantly varies. If attempts are made to precisely remove only noise, the delay time of the analog delaying circuit must be set with high accuracy. It is difficult for the analog delaying circuit using the Bessel type filters, which is formed on the semiconductor substrate, to satisfy this accuracy requirement.